Electrocardiography is an interpretation of the electrical activity of the heart captured by skin electrodes and externally recorded by an electrocardiograph, and the whole process is a non-invasive recording process.
During an electrocardiographic examination, lead wires are used to connect the electrocardiograph and the skin electrodes to a patient. A typical lead wire includes two metal lines: one is a signal line and the other is a ground line. The signal line and the ground line are separated by an insulating layer, so that the signal line and the ground line cannot touch each other. The signal line is connected to the patient by the skin electrodes and is the main part for transmitting the electronic heart signal; the ground line is connected to the ground of the electrocardiograph and is designed to cancel noises which may cause interference to the electronic signal transmission in the signal line.
When used in clinics, the lead wire is twisted every day when a nurse connects the skin electrodes to the patient, and the insulating layer between the signal line and ground line may break sooner or later. If the insulating layer is broken, the signal line may be connected with the ground line, which results in incorrect electrocardiogram output and a wrong diagnosis. When the insulating layer is broken and a short-circuit occurs between the signal line and the ground line (i.e. the signal line is connected with the ground line), the lead wire is referred to as a shorted lead wire. The shorted lead wire may cause intermittent signal loss, signal noise or decreased signal amplitude.
U.S. Pat. No. 3,602,215A1 provides an apparatus for detecting failure of a set of lead means used in conjunction with an EGG amplifier. The apparatus includes a constant current source connected to the individual lead means for generating a voltage representative of the transmission impedance of the lead means. Amplifying and level detecting means are connected to the lead means for generating trigger pulses indicative of lead failure whenever the transmission impedance of the lead means exceeds a predetermined magnitude. An indicator means driven by the trigger pulses is included to indicate the occurrence of lead failure.